1. Field of the Invention
The present invention relates to a recording/reproducing apparatus, a method of reproducing data, and a servo controlling method.
2. Discussion of the Related Art
An apparatus for recording/reproducing information on a recording medium such as a compact disc (CD) or a digital versatile disc (DVD), which is widely used, records the information on a single-layer recording surface of the recording medium or reproduces the information recorded on the single-layer recording surface. Storage capacity can be increased by laminating recording/reproducing surfaces of the recording medium, but the number of recording/reproducing surfaces which can be laminated in a single recording medium is four. Thus, there is a limitation in the increase of the storage capacity. Due to the limitation of the storage capacity, recently, storage technology using holography technology has been spotlighted.
The holography technology indicates the technology of reproducing an optical signal in an original form, that is, the technology of storing an interference pattern, which is generated by signal light having information and reference light irradiated at an angle different from that of the signal light, in a recording medium or reproducing information using the diffraction of the stored interference pattern. If the holography technology is used for recording data, since interference patterns can be recorded to overlap each other in a three-dimensional space in a thickness direction of the recording medium, it is possible to remarkably increase the storage capacity. That is, if the information is recorded while changing the incident angle, the phase and the wavelength of the reference light, it is possible to record holography information of several pages in a predetermined recording capacity. That is, it is possible to record holography information of a plurality of pages at any one position of a track of the recording medium.
In a reproducing apparatus for reproducing data recorded using the holography technology, in order to reproduce data of several tens or several hundreds of pages recorded in a predetermined area of the recording medium, a process of rotating the recording medium at a predetermined angle, stopping the recording medium and capturing reproduction light reflected from the recording medium should be repeated several tens times. Therefore, there is a need for a servo method which is applicable to a recording/reproducing apparatus using the holography technology. In the case where the holography technology using a recording/reproducing method different from other recording/reproducing methods is used, there is a need for an optical system or a recording/reproducing method suitable for the holography technology.